Talk:Functor hierarchy proposal

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Revision as of 21:46, 15 January 2007 by Twanvl (talk | contribs) (taking return out of Applicative)
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Um, it would be good if it was something like:

class (Idiom f) => Monad f where
  fmap f m = m >>= return . f -- or ap . return ?
  ap mf mv = mf >>= \f -> mv >>= \v -> return $ f v
  (>>=) :: f a -> (a -> f b) -> f b

Or am I missing the point?

Serhei 15:24, 29 January 2006 (UTC)

You can't put defaults for one class in another. Though that could be another proposal. —Ashley Y 21:02, 29 January 2006 (UTC)
Wasn't this part of John Meacham's class system proposal? What happend to this? -- Wolfgang Jeltsch 19:25, 2 February 2006 (UTC)

<*> should really be merged with ap, right ? (Btw, why such a symmetric operator symbol as <*> ? <* or some other assymetric one would be better .. even plain `ap` is not so bad, imho.)

Also, it would be nice to change sequence, sequence_, mapM and mapM_ to only require Applicative instead of Monad. (Or one could merge these four into something like Data.FunctorM.FunctorM, which should use Applicative anyway.) -- StefanLjungstrand 10:18, 3 November 2006 (UTC)

I think it makes sense to take return out of Applicative. Either into a separate step between Functor and Applicative, or into a new class altogether:

class Boxable f where
     return :: a -> f a
class (Functor f, Boxable f) => Applicative f where

But maybe this is just overengineering.

Twanvl 21:46, 15 January 2007 (UTC)